Building on the work of the FOSScar project, the pair needed a way to burn the PLA out of a mold with a microwave. The trick is to use a susceptor. Susceptors convert the microwave’s RF energy into thermal energy exactly where it is needed. If you’ve ever nuked a hot pocket, the crisping sleeve is lined with susceptor material. After trying several materials, [Julia and Mason] settled on a mixture of silicon carbide, sugar, water, and alcohol for their susceptor.

The actual technique is pretty simple. A part printed in PLA is coated with susceptor. The part is then placed in a mold made of plaster of paris and perlite. The entire mold is cooked in an unmodified household microwave to burn out the PLA.

A second microwave with a top emitter is used to melt down aluminum, which is then poured into the prepared mold. When the metal cools, the mold is broken away to reveal a part ready to be machined.

We think this is a heck of a lot of work for a single part. Sometimes you really need a metal piece, though. Until metal 3D printing becomes cheap enough for everyone to do at home, this will work pretty well.

As a maker, [Sefi] was always building things which impressed [Tania], so he thought it was only fitting to make the proposal a one-of-a-kind maker experience.

He started by designing the engagement ring himself, to be 3D printed. It’s an amazingly complex little thing made up of the repeating words of the quote “I will betroth you to me forever”. It was almost too complex in order to print — but they managed to do it in wax, which allowed them to create a mold and then cast the final part in white gold. Once complete, they set a diamond in place to cap it all off.

The second step was the proposal, which was made possible using a quadrotor, a strip of RGB LEDs, and a long camera exposure. To show it off in real-time to [Tania] they setup a projector and screen on the side of the street, providing a surreal window into the park behind them. It was all made possible with the help from over 20 people from the XLN Makerspace and SkyLens (the quadrotor people).